Caterpillar Inc. of Peoria, Ill. makes a variable speed clutched fixed pitch fan (CAT fan). As an engine to which the fan is attached speeds up, the fan clutch begins to slip, thus maintaining the fan at a desired rpm, avoiding power waste and excessive noise.
There are various variable pitch fans known, as for example those described in U.S. Pat. Nos. 5,564,899; 5,022,821; and 5,122,034. It is an object of the invention to provide improved operating features for variable pitch fans.